Our present invention relates to a method of operating a rolling train, especially for the production of structural shapes. The invention also relates to a rolling method, to a control system for a rolling line or train and to a rolling train provided with that control system. Specifically the invention deals with the rolling in a succession of mill stands, of an elongated workpiece to produce a structural shape, also referred to as a profiled product.
In the production of structural shapes, rolling mill stands may be grouped together or arrayed in a rolling train and the elongated workpiece is passed in succession through these mill stands to reduce the cross section of the workpiece from stand to stand and thereby impart a particular configuration or profile to that workpiece in producing the rolled product. The rolled product may be composed of steel and the number of roll stands and the configurations of the rolls therein may vary depending upon the product produced and the size of the product.
Each roll stand is operated with a number of operating parameters which can include temperatures, speeds, rolling forces and, of course, such parameters as gap width and roll position, all of which or some of which may be controlled by effectors, for example, servomotors which may be fluid-operated or servovalves. The operating parameters can be adjusted in accordance with a setpoint value and it is known to provide the rolling stands with controls for supplying the setpoint values for a variety of such operating parameters.
The generally elongated workpiece is passed through the succession of mill stands in a rolling direction and a number of mill stands thus are disposed in succession in this direction so that the rolls of this mill stand can engage the workpiece in succession or one after the other and either at the same time or after the workpiece has left a preceding mill stand and entered a succeeding mill stand. The workpieces can be shaped in a single pass through the rolling mill train or in multiple passes.
A rolling train having a multiplicity of such stands is commonly used for the shaping of profiled rolled products or structural shapes and the profiled rolled product can be a so-called xe2x80x9cheavy profilexe2x80x9d with a U cross section or a double-T cross section or I-beam or H-beam cross sections. These cross sections have a web, usually the base of the channel for U-shaped cross sections and the central member of the H-beam or I-beam, and flanges which extend perpendicularly to one or both sides of the web.
In the shaping of such profiled workpieces in rolling mills, so-called universal mills are used at least in part. A universal mill comprises generally two horizontal rolls which are paired to roll the web of the structural shape and have a gap between them which is adjustable and determines the web thickness and a pair of vertical rolls which engage the opposite sides of the workpiece and determine the overall width of the structural shape produced.
These vertical rolls are usually disposed within the universal stand and can be located somewhat offset from the pairs of horizontal rolls.
In the operation of rolling lines with such mill stands, especially universal mills, each mill stand is supplied with setpoint values for a number of its operating parameters which are selected so that the product, upon rolling in that mill, will approach the setpoint profile of the desired product as closely as possible. These setpoint values adjust the mill, therefore, for the web thickness, the flange thickness, the rolled product width and like dimensions of the finished product. The setpoint values may be, for example, hydraulic pressures for the hydraulic controllers of roll positions or for the desired rolling forces.
In modern rolling trains, it is not uncommon to utilize derivative and comparatively complex operating parameters rather than simple parameters like roll positions, these more complex parameters taking into consideration factors such as temperature, gap cross sections and the like.
In any case it is important that the setpoint parameters which are applied to a particular mill stand be capable of producing a rolled product which is comparatively close in profile to the desired shape with dimensions within a limited tolerance range. However it is difficult to maintain comparatively narrow tolerances since during the rolling operation itself, various influences on such parameters arise and change in a relatively uncontrollable manner. As a consequence it is necessary to carefully monitor the rolling process and most commonly the operators are required to vary practically continuously the operating parameters applied to the mills during the rolling of a given workpiece or a series of such workpieces or even from workpiece to workpiece. In spite of these efforts, however, a high degree of precision and practically narrow tolerances cannot be satisfactorily maintained or can only be maintained with considerable expenditure of effort or with especially extensive equipment.
It is, therefore, the principal object of the present invention to provide an improved method of operating a rolling train of the above-described type and particularly for the production of structural shapes and especially heavy structural shapes such as channel, double-T girders, H-beams and I-beams, whereby drawbacks of earlier systems are avoided.
It is a particular object of the invention to provide a method of controlling a rolling train for such purposes whereby a comparatively low capital and operating cost, it is possible to obtain especially narrow tolerances in the production of profiled rolled products, i.e. structural shapes.
Another object is to provide a control system for a rolling mill train which allows narrow tolerances which establish and hold more reliably than with earlier systems.
A further object of this invention is to provide a rolling mill train for the rolling of structural shapes whereby drawbacks of earlier systems are avoided.
These objects and others which will become apparent hereinafter are attained, in accordance with the invention, in a method of operating a rolling mill train for producing structural shapes, especially heavy structural shapes or profiled products which comprises the steps of:
(a) rolling a workpiece in a succession of mill stands, each equipped with a plurality of working rolls engaging the workpiece to reduce a cross section thereof in a configuration of a structural shape to be produced, each of the mill stands having a plurality of adjustable operating parameters determining the rolling process in the respective mill stand;
(b) detecting a profile of a structural shape produced by the succession of mill stands and comparing the detected profile with a set-point profile corresponding to a structural shape to be produced;
(c) deriving from the comparison of the detected profile with the setpoint profile respective corrective setpoint values for each of the parameters determined by deviation of the detected profile from the setpoint profile;
(d) weighting each of the corrective setpoint values with a weighting factor specific to the respective mill stand to produce weighted corrected setpoint values for each of the parameters; and
(e) adjusting the operating parameters of each of the mill stands with the respective weighted corrected setpoint values.
According to the invention the corrected setpoint values for at least one of the mill stands include a setpoint value for at least one structural shape dimensional parameters selected from a web thickness, a flange height and a flange thickness.
The corrected setpoint values can include setpoint values for each of the key structural shaped dimensional parameters, namely, flange height, flange thickness and web thickness.
According to another feature of the invention each of the mill stands is controlled individually by respective determinations of deviations of detected profiles from setpoint profiles for the respective mill stands, derivation of respective corrective setpoint values, weighting of the corrective setpoint values with respective mill-stand-specific weighting factors, and adjustment of the operating parameters of each individual mill stand with the respective weighted corrected setpoint values.
The rolling mill train according to the invention can comprise:
a succession of mill stands, each equipped with a plurality of working rolls engaging a workpiece to be rolled in the stands to reduce a cross section thereof in a configuration of a structural shape to be produced, each of the mill stands having a plurality of adjustable operating parameters determining the rolling process in the respective mill stand;
at least one sensor for detecting a profile of a structural shape produced by the succession of mill stands and comparing the detected profile with a set-point profile corresponding to a structural shape to be produced;
means for deriving from the comparison of the detected profile with the setpoint profile respective corrective setpoint values for each of the parameters determined by deviation of the detected profile from the setpoint profile and for weighting each of the corrective setpoint values with a weighting factor specific to the respective mill stand to produce weighted corrected setpoint values for each of the parameters; and
means for adjusting the operating parameters of each of the mill stands with the respective weighted corrected setpoint values.
The control system for the purposes of the invention can comprise at least one sensor for detecting a profile of a structural shape produced by the succession of mill stands and comparing the detected profile with a setpoint profile corresponding to a structural shape to be produced, a computer connected to the sensor for comparing the detected profile with the setpoint profile and deriving respective corrective setpoint values for each of the parameters determined by deviation of the detected profile from the setpoint profile, means for weighting each of the corrective setpoint values with a weighting factor specific to the respective mill stand to produce weighted corrected setpoint values for each of the parameters, and means for adjusting the operating parameters of each of the mill stands with the respective weighted corrected setpoint values.
According to the invention, therefore, the profile of the rolled product emerging from the rolling train is detected and compared with a setpoint profile and one or more setpoints of one or more rolling mill stands is corrected based upon the deviation of the detected profile from the setpoint profile and is weighted by a mill-stand-specific weighting factor to serve as the weighted corrected setpoint which is applied to the effector of that mill stand for control purposes.
The setpoint profile may be contained in memory of a computer serving for the comparison and weighting factors may also be in electronic storage. The computer can generate, therefore, not only the corrected parameter value but also the weighted corrected value as a function of the stored information.
The invention is based upon the concept that it is possible to maintain especially narrow tolerances with respect to the profile of the rolled product when this profile is continuously monitored and evaluated as soon as possible after being imparted to the workpiece and directly upon rolling, especially during the ongoing rolling process. In that case, deviations of the actual produced profile from the predetermined setpoint profile can be detected during the production of the rolled product and these deviations can be utilized to generate appropriate corrective values to compensate for the setpoint value. The correction value can be supplied as an additional setpoint value and can be utilized in control as soon as appropriate measured values for the actual profile are obtained. The generation of the additional setpoint values, i.e. the corrected setpoint values, can be length synchronized, i.e. can be synchronized with the length of the workpiece as it is being rolled so that corrections can be made for corresponding portions of the length. Alternatively, or in addition, they may be time synchronized so that the adjustments of the mill stands are made for corresponding points in time during the rolling process.
Especially high precision can be obtained if the corrected setpoint values are applied to effect correction at as close as possible to the location in which the deviation from the setpoint profile arises.
The tolerance-existing deviations in the profile of the rolled product which is produced may stem from a number of sources, namely, from each of the mill stands traversed by the rolled product and can be cumulative in the product leaving the rolling trains. Such cumulative deviations are readily ascertained by comparing the actual profile with the setpoint profile and require a single and simple measurement system. However, the corrections must be distributed to the individual mill stands at which the errors arise and this is achieved, in accordance with the invention by providing mill-stand-specific weighting factors for the corrected setpoint values which are fed back to the mill stands. These weighting factors, representing the contribution of each mill stand to a potential defect can be varied during the course of rolling based upon the measurements made and thus represent a learning function or a self-optimizing function which can eventually reduce any deviations from the setpoint profile to those which lie within the acceptable tolerances.
The correction of the weighting factors can be effected continuously or at regular intervals and can be effective for each subsequent rolling operation based upon a preceding rolling operation.
The maintenance of especially narrow tolerances is enabled by ensuring substantially constant tension-compression ratios in the rolled product between successive roll stands. To support this condition advantageously, a data exchange is provided between the control system providing weighted corrected setpoint values for the mill stand and a tension-compression control for the mill stand. The production of weighted corrected values for the setpoint is most effectively accomplished as close as possible in time to the comparison of the setpoint profile with the profile and thus in a kind of on-line control. Thus while a workpiece is in a mill stand, the head thereof which has emerged, can already be measured so that corrected setpoint values can be fed back to the mill stand for adjustment while the balance of the workpiece continues to be rolled thereby. In that case, corrections can be achieved between the rolling of the head of the rolled product and middle and end portions thereof.
The method of the invention has been found to be especially suitable for the operation of a rolling mill train for the production of double-T girders. Such a rolling train has at least one so-called universal mill stand having both a pair of horizontal rolls and a pair of vertical rolls. In this rolling train, preferably the setpoints for the operating parameters of web thickness, plan head and/or flange thickness are controlled with appropriate weighted corrected setpoint values and are maintained with especially narrow tolerances. It is precisely the profile of a double-T girder which has a central web flanked by transverse flanges on either side which admits of rolling under such controlled conditions. The web thickness, flange height and flange thicknesses practically completely define the double-T girder. The adjustment of the web thickness can be achieved by a corresponding adjustment of the rolling gap between the horizontal rolls of the universal stand. The universal stand can be controlled so that a setpoint value is provided for the web thickness and this setpoint value can be used to adjust the stand directly or through derived operating parameters, for example, through position settings of the individual horizontal rolls.
According to a feature of the invention, the respective mill-stand-specific weighting factors are dependent upon the rolled product and material. As a consequence, the contribution of each mill stand to the total deviation of the rolled product from the setpoint product and which is a function both of the characteristics of the mill stand and its role in the rolling process, as well as of the material rolled, will reflect all of these factors and not be exclusively a function of the position of the respective mill stand in the train. The corrected setpoint is applied to the mill stand with or in place of the corresponding original setpoint and will reflect the weighting factor as well.
The horizontal rolls which cooperate in each roll stand to define the web of the rolled product can be adjusted together. It is possible for example to symmetrically and simultaneously adjust the pairs of horizontal rolls each with a single setpoint value, especially a setpoint value controlling the rolling pressure or force. Of course it is possible to adjust each of these rolls independently with respect to an imaginary reference plane midway between them. The horizontal rolls of the separate mill stands can be separately adjustable or, if appropriate, adjusted by common setpoint values appropriately weighted for the respective mill stands. In principle, the rolls can be adjustable independently from one another so that the setpoint inputs to them may reflect absolute values of their positions with respect to a reference plane or a number of reference planes, such as the rolling plane, and absolute values of the rolling gaps. With the system of the invention, however, there is considerable flexibility since the corrected setpoints for the different stands are weighted separately and can be used to adjust individual rolls. The invention, as a consequence, contributes a higher degree of freedom in controlling the various parameters to which the mills respond and enable the greater flexibility to be used to maintain especially narrow tolerances. The compensation for rolling defects with the invention, therefore, is not only possible between the stands but within each individual stand and among the independently adjustable rolls of each individual stand.
To avoid overcompensation of rolling defects in a reliable manner, especially where there is a danger that any modified setpoint application might be excessive from point of view of the acceptable tolerances, each corrected setpoint value is advantageously limited to a parameter specific maximum value. Alternatively or in addition, it has been found to be advantageous to supply a corrected setpoint value for a horizontal adjustment and a corrected setpoint value for a vertical adjustment of a particular roll stand in which the ratio of the corrected setpoint values are limited to a predetermined maximum.
The corrected values can be determined based upon previous rolling processes. For instance, a number of previous rolling results can be evaluated and for each of them the profile of the rolled product can be determined and based upon the difference between the setpoint and actual profiles in each of those cases, by averaging or by some other algorithm, the corrected value can be determined either automatically or with the intervention of a service person. For example a correction can be undertaken when the sum of corrected values or corrections exceed a predetermined limiting value. Of course it is possible to generate the corrected setpoint value directly from a single preceding rolling operation and even on the fly within a single operation as has been noted or to use an immediately preceding rolling operation or the one in progress in a more highly weighted contribution to the correction. The results can be the basis for presetting the rolls for the next rolling operation or a newly introduced workpiece for which there may not yet be an evaluatable actual value of a setpoint or profile. However, it is preferred, whether or not inputs are provided from preceding passes or preceding rolling operations, always to provide a certain portion of the length of the rolled product as a test piece which is compared with the setpoint profile and to utilize a correction in the further rolling of the workpiece.
In the production of double-T girders especially, it has been found to be advantageous to utilize a reversing rolling process in which the workpiece is passed repeatedly through the roll train back and forth so that the movement of the workpiece through the mill stands is a kind of oscillating movement. In a first pass in one direction, a cross section reduction is effected and a cross section reduction is then effected upon movement of the workpiece through the mill stand in the opposite direction. This can be repeated any number of times with adjustment of the mill stand rolls between such passes and before the workpiece is then forwarded onto another group of mill stands or another mill stand, for final rolling therein. In that case, a detection of the profile of the workpiece can be effected at an intermediate stage between, for example, repeated passes of the workpiece through the mill stands and compared with the setpoint profile to generate the corrected setpoint values. This approach has been found to allow very narrow tolerances to be maintained. The settings of the mill roll of each subsequent pass can be determined by the measurement from a previous pass by way of example. The corrected setpoint value thus represents in each case an adaptation of the setting previously provided and is determined by a combination of the original setting and the corrected value.
This type of adaptation is rolling-pass dependent and can also be rolled-product dependent. The adaptation enables an especially rapid reaction or compensation when rolling to defects as they arise. To detect the actual profile of the rolled product after each pass in one direction or the other, on both sides of the plurality of rolling stands which are traversed by the rolled product on each pass, respective measuring devices are provided to detect the contour of the rolled product of that pass. An especially simple construction, however, utilizes a single measuring device or system which can advantageously be provided downstream of the set of roll stands in the original or initial rolling direction, i.e. immediately downstream of the last of the plurality of rolled stands which are traversed by the workpiece. In such a configuration of the apparatus, the adaptation can be effected after a xe2x80x9cpass xxe2x80x9d, i.e. the evaluation of the actual rolled product profile can be effected after each xth pass through the respective rolling mill or group of mill stands and thus for pass x, pass x+2 and thereafter every further second pass. In the passage in the opposite direction, i.e. the x+1 pass, to minimize any effect of error and without requiring a measurement to the workpiece upon the completion of that pass, we operate by interpolation between the previous corrected value and an expected or probably value for the next x+2 pass to determine a probably value for the intervening x+1 pass.
The control system for the rolling train of the invention can comprise a controller which is usually a computer which can be programmed as to the setpoint value which is expected after each pass or each x+2 pass, as discussed, or is provided with a memory bank containing the setpoint profile data. The computer is connected to the measuring device or devices which detect the actual profile or characteristics of the actual profile which can be compared with the setpoint value described. The memory or storage can also include stand-specific weighting factors and these can be tapped from memory based upon the stand through which the workpiece is passing at any given moment.
The corrections can be made on the fly or between passes or after the rolling of a workpiece and before the rolling of the next workpiece.
With the system of the invention, the weighting factor specific to the particular mill stands are used in calculating the corrected setpoint values which enables error compensation where those errors occur or so as to prevent those errors from occurring, thereby precluding accumulation of errors from contribution of the various roll stands in the roll product. The individual roll stands are controlled individually or in groups based upon the calculated corrections with the weighting factors so that practically complete compensation for errors can be ensured and especially narrow tolerances can be maintained. Since the adjustment and determination of the corrected values can be effected automatically, the involvement of service personnel is held to a minimum and the need for sampling of the workpiece can be minimized as well. The occasions on which the mill train must be brought to standstill because tolerances are exceeded can be reduced, if not eliminated entirely and the roll train thus can have an especially high throughput and productivity.